International Journal of Trend in Scientific Research and Development (IJTSRD)
Volume 3 Issue 5, August 2019 Available Online: www.ijtsrd.com e-ISSN: 2456 – 6470
Design of Active Filter for Reducing Harmonic
Distortion in Distribution Network
Khine Zar Maw
Department of Electrical Power Engineering, West Yangon Technological University, Yangon, Myanmar
How to cite this paper: Khine Zar Maw
"Design of Active Filter for Reducing
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IJTSRD26663
Issue-5,
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https://doi.org/10.31142/ijtsrd26663
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ABSTRACT
Power transmission and distribution systems are designed for operation with
sinusoidal voltage and current waveform in constant frequency. Power
electronic control devices due to their inherent non linearity draw harmonic
and reactive power form the supply mains. The wide use power electronic
equipment with linear load causes an increasing harmonics distortion in the ac
mains currents. Harmonics component is a very serious and harmful problem
in the
distribution system. The main adverse effects of harmonic current and voltage
on power system equipment are overheating, overloading, perturbation of
sensitive control and electronic equipment, capacitor failure, communication
interferences, process problem, motor vibration, resonances problem and low
power factor. This paper describes the modelling of active filter with
synchronous d-q reference frame theory for harmonic compensation in
distribution systems. The case study is carried out at Hlaingtharyar township
distribution system. The model is implemented for harmonic analysis from
simulation using a Matlab/Simulink with the THD values obtained by practical
measurement.
KEYWORDS: Electrical Distribution System, Sinusoidal voltage Nonlinear Load,
Total Harmonic Distortion, Active Filters
I.
INTRODUCTION
In electrical power system, power harmonics has become a
serious problem nowadays. The electrical power system
normally operates at 50 Hz frequency. However, saturated
devices such as transformers, arcing loads such as florescent
lamp and power electronic devices will produce current and
voltage components with frequencies higher than the
fundamental frequency into the power line. These higher
frequencies of current and voltage components are known as
the power harmonics.
Harmonic distortion can cause severe disturbances to
certain electrical equipment’s requirements. The harmonics
have the following problems on normal operation of
distribution power system.
1. Relay malfunction,
2. Transformer hum,
3. Shutdowns,
4. Metering and Telecommunication interference,
5. Overheating of transformers,
6. Overloading of neutral conductor,
7. Three phase unbalance,
8. Distorted supply voltage, and
9. Shortening life span of electrical installations.
The distribution substation has to limit the harmonic
currents by controlling their loads and the utilities should
limit the harmonic voltages by controlling the power system
impedances. This is to ensure to carry their responsibility on
controlling the harmonics level in the power system. The
IEEE 519-1992 standards demand that the total harmonic
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distortion (THD %) produced by electrical equipment should
not be higher than the defined limits of the standards. THD is
a power quality term that is used to define the amount of
distortion in voltage or current waveform .The higher the
percentage of the value of THD, the less efficiency of
equipment in the distribution system becomes.
II.
HARMONICS DISTORTION
Harmonics are the major source of periodic waveform
distortion. Harmonics distortion is the change in supply
waveforms from the ideal sinusoidal waveform. Harmonics
distortion can be expressed as a summation of sinusoidal
waves as described in Figure 2.1. The distortion occurs when
non-linear loads distort the fundamental sinusoidal current.
This distorted current is conducted through the system
network, and when distorted current travels through the
linear components in the system network, it produces
distorted voltage.
Figure2.1. Fourier series Representation of a
Distorted Waveform
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Current harmonics affect the distribution system by loading
the system when the waveforms of other frequencies use the
same system capacity without contributing any power to the
load. They also increase the system copper losses. However,
current harmonics cannot affect directly the linear loads in
the system but the non-linear loads that cause current
harmonics are affected.
On the other hand, voltage harmonics affect the entire
system, not just the non-linear loads, and their impact
depends on the distance between the power source and the
harmonics-causing.
III.
HARMONIC POLLUTION INDICES
The total harmonic distortion (THD) is the most common
measurement indices of harmonic distortion. THD applies to
both current and voltage and is defined as the root meansquare (rms) value of harmonics divided by the rms value of
the fundamental, and then multiplied by 100% as shown in
the following equation: To provide a reference guide for both
utilities and their customers, many international standards
have been proposed, such as IEEE-519 and IEC 61000-4-7.
According to these standards, harmonics pollution should
not exceed certain limits. These limits have been specified
using harmonics indices. Total harmonics distortions (THD)
are the most widely used harmonics indices.
A. Total Harmonics Distortion (THD)
According to IEEE-519 standards, total harmonics distortion
is defined as the summation of the effective value of the
harmonics components in the distorted waveform relative to
the fundamental component. It can be calculated for either
voltage or current.
[1]
where,
Vh = the RMS value of voltage harmonics component h, Ih =
the RMS value of current harmonics component h;
IV.
HARMONIC MITIGATING TECHNIQUES
Any combination of passive (R, L, C) and active (transistors,
op-amps) elements designed to select or reject a band of
frequencies is called a filter. Filters are used to filter out any
unwanted frequencies due to nonlinear characteristics of
some electronic devices or signals picked up by the
surrounding medium. Filters are one of those corrective
(remedial) solutions aimed at overcoming harmonic
problems and to keep them within safe limits.
To reduce the harmonics conventionally passive L–C filters
were used and also capacitors were employed to improve
the power factor of the ac loads. But the passive filters have
several drawbacks like fixed compensation, large size and
resonance problem. To mitigate the harmonics problem,
many research work developments are developed on the
active power (APF) filters or active power line conditioners
[10].The active power filter (APF) is a popular approach for
cancelling the harmonics in power system. The main
component in the APF is the control unit.
To cancel the harmonics and compensate the reactive power
APF is the suitable solution. The APF concept is to use an
inverter to inject currents or voltages harmonic components
to cancel the load harmonic components. The more usual
configuration is a shunt APF to inject current harmonics into
the point of common coupling (PCC). The APF can be
installed in a low voltage power system to compensate one
or more loads; thus, it avoids the propagation of current
harmonics in the system. The developments of different
control strategies give APF to a new location. As APF
compensate the reactive power and cancel the harmonics, it
is also called as active power line conditioners (APLC). The
operation of APF depends on algorithm to controller.
A. Synchronous reference frame method
Synchronous reference frame method is based on the
transformation of vectors into synchronously rotating direct
(d), and quadrature axis (q) reference frames.
The following Figure 3.6 shows the principal of Synchronous
reference theory based control in active filter.
The THD for current is as follows:
∞
∑ I 2h
THDi =
h=2
I1
× 100%
[2]
THD of current varies from a few percent to more than
100%. THD of voltage is usually less than 5%. Voltage THDs
below 5% are widely considered to be acceptable, while
values above 10% are definitely unacceptable and cause the
problems for sensitive equipment and loads [8]. The main
problem of harmonics is voltage waveform distortion by
calculation the relation between the fundamental and
distorted waveforms by finding the square root of the sum of
the square of all harmonics generated by a single load, and
then dividing this number by the nominal 50 Hz waveform
value.
Most international standards use these indices to determine
the total acceptable harmonics distortion limit and the
individual harmonics distortion ratio for each effective
harmonic; both individual and total harmonics distortion
measurements should be within the standard limits
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Figure4.1. Principal of Synchronous Reference Theory
Based Control
Among them, Filters may reduce harmonic levels to below
IEEE 519-1992 guidelines. The harmonic limit
recommendations that are the Total voltage distortion
(THD) is 5.0% and the total current distortion level is 4% in
distribution system.
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V.
CASE STUDY
The distribution system under study is shown in fig (5.1). The detailed study is carried out at Hlaingtharyar
distribution substation No (1).
Fig.5.1 [a] Sinle Line Diagram of No 1. Transformer in Hlaingtharyar Substation (1)
Fig.5.1 [b] Single Line Diagram Of No 2. Transformer
In Hlaingtharyar Substation (1)
The substation is located at Hlaingtharyar Township, Yangon, Myanmar. This substation is constructed for supplying the
electric power to Hlaingtharyar industrial zone and some housing of Hlaingtharyar. Hlaingtharyar Industrial Zone is the largest
one in Myanmar. Since the dominant load of this substation is industrial load. The incoming line of substation No (1) is taken
from 33 kV bus of Hlaingtharyar Primary substation which is located at west of Hlaingtharyar township. Substation No (1)
comprise two number of 20 MVA, 33 kV/ 11 kV transformers. There are eight number of 11 kV main distribution feeder which
are connected to two separate 11kV bus bar of substation No (1) as shown in Figure (5.1). The different types of linear and nonlinear loads are connected to the system. The Figure 5.1 is showing the single line diagram of Hlaingtharyar substation (1). The
following table are showing the total voltage and current harmonic distortion levels in Hlaingtharyar substation (1).
Table 5.1. Voltage and Current Distortion in Hlaingtharyar Distribution Networks
Harmonic orders h=5 h=7 h=11 h=13 TOTAL HARMONIC DISTORTION (%)
THDV
8.69 3.72 3.50
2.72
10.68
THDi
3.9 1.19 0.71
0.47
4.17
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The results show that the harmonic distortion exceeds the permissible limits for voltage and current in PCC. The more salient
orders are the 5th, 7th, 11th and 13th harmonic orders. The simulation waveform without filter in pcc is shown in figure5. 2.
Fig.5.2. Simulation Waveform Results Without Filter In PCC
VI.
THE DISTRIBUTION SYSTEM WITH ACTIVE FILTER
The mitigation method is active filter based on d-q methods for maintaining sinusoidal source currents when the source
supplying a non-linear load. And then, they are installed at the PCC in the Hlaing Tharyar substation (1). The complete model of
active power filter is presented in Figure 6.1 and results were obtained by using MATLAB/Simulink Sim power system Toolbox
software for a APF compensating harmonics produced by Non-linear loads.
A. Calculation for capacitance and reactance of active filter
The reactive power demand of the system without harmonic filter is 10.99 MVAR.
QC supply by filter = 0.3× 10.99 = 3.3 MVAR.
XC =
V2
50002
=
= 7.576Ω
QC 3.3 ×106
For PWM generator, the switching frequency is set as 1080 Hz. Thus the required capacitance is obtained as follows:
C=
1
1
=
= 1.945 × 10 −5 F ≈ 20 µF
2π f X C 2 × π × 1080 × 7.576
40 % ripple of Iout, inductor size is obtained as follows;
L=
( 19.05k - 5k) × 5k
= 6.94mH
19.05k × 1080 × (0.4 × 1230.4)
Thus, 7 mH inductor is selected for active filter.
B. Synchronous Method Active Filter using d-q-0 Theory
For PI controller, the values of Kp and Ki are chosen and these are shown as follows:
Kp
= 0.0016
Ki
= 0.00015
Figure6.1. Simulink Diagram of Synchronous Method Active Filter using d-q-0 Theory
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VII.
CASE STUDY
Fig.7.1. Modelling of Hlaing Tharyar Substation (1) with Active filters
The following Table 7.1 is showing the total harmonic
voltage and current distortion with filters.
5000
4500
4000
Table7.1. Voltage and Current Distortion in Hlaingtharyar
Distribution Network
Harmonic
h=5 h=7 h=11 h=13 Total
orders
THDv
0.24 0.15 0.14
0.09
0.91
THDi
0.19 0.08 0.05
0.03
0.26
After installing the active filters, the THD % of voltage and
current are changed and declined in HTY network. The
THDv% is 0.91% and THDi% is 0.26% at PCC in HTY
network.
3000
2500
2000
1500
1000
500
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Figure7.3. DC Voltage with Active Filter for Case Study
In simulation result, the dc voltage is reached the steady
state at 1.5 sec when the Kp is 0.0016 and Ki is 0.00015 for PI
controller.
Table7.2. Total Harmonic Distortion Without and With
Filters in HTY Substation (1)
System without
System
System with
mitigation techniques
active filter
(%)
THDv %
10.68
0.91
THDi %
4.17
0.26
4
3
3500
x 10
V
2
1
0
600
I
400
200
0
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
Time (sec)
Figure 7.2.Three Phase RMS Voltage and Current
Waveforms with Active Filter
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According the Table 7.2, the active filter is more effective
compensation of harmonics in this network. The percentage
of total harmonic voltage distortion with active filter is
reduced to 0.91% and current is reduced to 0.26 % which
are very lower than the harmonics limit 5% imposed by the
IEEE standard.
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VIII.
DICUSSIONS
Under Substation (1) distribution network is increasing the
non-linear loads, distorted voltage and current are cause to
be harmonics. That can be effected power system quality and
reduced the power system performance. The control or
mitigation of the power quality problems may be realized to
use mitigation techniques applied in distribution system.
The mitigation technique is active filtering method that may
reduce harmonic levels to below IEEE 519 guidelines.
IX.
CONCLUSIONS
The harmonic level has a great effect on the performance of
the system components and equipment’s. Harmonic analysis
for the distribution system is necessary for appreciating
system operation and upgrade. In Hlaingtharyar Substation
(1) has the voltage distortion level is 10.68% and current
distortion is 4.17% according to measure without filters.
After installing filters, the voltage distortion will be 0.19%
and current distortion is 0.26%. The results of THD are
significantly decline in Hlaingtharyar Substation.
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ACKNOWLEDGMENTS
The author wishes to express her deepest gratitude to her
dear parents for their support, help and giving suggestions.
Similar thanks to my son and daughter because of my
vitamins when I feel tired.
REFERENCES
[1] J. Arrillaga, D.A. Bradley, and P.S Bodger, Power System
Harmonics. New York: John Wiley & Sons, 1985, pp. 5135.
[2] IEEE Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems”. IEEE Std
519 – 1992.
[3] IEEE/CIGRE Joint Task Force on Stability Terms and
Definitions, “Definition and Classification of Power
System Stability”, IEEE Trans-actions on Power Systems,
Vol. 5, No. 2, May 2004, pp. 1387–1401.
[4] “IEEE Recommended Practice for Electric Power
Distribution for Industrial Plants”, IEEE Std 141-1993
(Revision of IEEE Std 141-1986
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